Set Methods

Question 1

Points to Note about HashSet

Answer 1

A. HashSet doesn’t maintain any order, the elements would be returned in any random order.
   B. HashSet doesn’t allow duplicates. If you try to add a duplicate element in HashSet, the old value would be overwritten.
   C. HashSet allows null values however if you insert more than one nulls it would still return only one null value.
   D. HashSet is non-synchronized.
   E. The iterator returned by this class is fail-fast which means iterator would throw ConcurrentModificationException if HashSet has been modified after creation of iterator, by any means except iterator own remove method.

Question 2

Declaring HashSet

Answer 2

HashSet hashset = new HashSet();

Question 3

Add an Item to Hashset

Answer 3

hashset.add(“Element”);

Question 4

Remove an Item to Hashset

Answer 4

hashset.remove(“Element”);

Question 5

Clearing all element from a HashSet

Answer 5

hashset.clear();

Question 6

Iterating over an HashSet (Forward)

Answer 6

Method 1 - ITERATOR 
Iterator iterator = hashset.iterator();
    while (iterator.hasNext()) {
       System.out.println(iterator.next());
    }

Question 7

Does the HashSet contains this Item ?

Answer 7

hashset.contains(“Element”);

Question 8

Is the HashSet empty ?

Answer 8

hashset.isEmpty();

Question 9

Whats the length/size of the HashSet?

Answer 9

hashset.size();